1. Field of the Invention
The present invention relates to a gap adjusting device for adjusting a gap defined between a recording head and a recording medium on which recording is to be performed, and a recording apparatus including such gap adjusting device. The present invention also relates to a liquid ejection apparatus.
The liquid ejection apparatus in the present application includes but not limited to a recording apparatus which uses an ink-jet type recording head and achieves printing on the recording medium by ejecting ink from the recording head, such as a printer, a copier and a facsimile machine, as well as an apparatus which uses a liquid ejection head corresponding to the ink-jet type recording head and ejects liquid suitable for an application of the apparatus in place of the ink from the ink ejection head to a medium, thereby causing the liquid to adhere to the medium.
Examples of such a liquid ejection head include a color-material ejection head used in fabrication of color filters for a liquid crystal display or the like, an electrode-material (conductive paste) ejection head used in formation of electrodes for an organic EL display or a field emission display (FED), a biological organic material ejection head used in fabrication of bio-chips, and a sample ejection head as a precise pipette, other than the aforementioned recording head.
2. Description of the Related Art
As an exemplary recording apparatus, an ink-jet printer is known in which an ink-jet recording head is provided on the bottom of a carriage that reciprocates in a main scanning direction. The carriage is caused to reciprocate in the main scanning direction by a driving force of a motor, while being guided by a carriage guide shaft extending along the main scanning direction.
In order to perform printing appropriately for each of recording media that are different in thickness, the ink-jet printer includes a gap adjusting device for adjusting a gap between the ink-jet recording head and the recording medium. The gap adjusting device includes a bushing member at an end of the carriage guide shaft, which has its center of rotation at a position away from a shaft center of the carriage guide shaft. By rotating the bushing member, the level (height) of the carriage guide shaft is moved up and down. See Japanese Patent Application Laid-Open No. 8-300769. Moreover, Japanese Patent Application Laid-Open No. 10-211748 describes that a plurality of (two, for example) carriage guide shafts are provided and bushing members respectively provided at shaft ends of the carriage guide shafts are rotated in synchronization with each other, thereby moving the carriage guide shafts up and down simultaneously.
The most of the gap adjusting devices conventionally known, including the aforementioned gap adjusting devices, are arranged to have two gap adjusting positions that are switched by an adjusting lever or the like. The adjusting lever is arranged to engage with the bushing member and rotate the busing member. See Japanese Patent Application Laid-Open No. 2002-36660. Alternatively, the two gap adjusting positions are switched by using the driving force of the motor, as described in Japanese Patent Application Laid-Open No. 10-211748. In this case, each of the two gap adjusting positions is kept by a force applied by a coil spring.
More specifically, the coil spring that engages with the adjusting lever is provided in such a manner that the forcing direction is changed at an intermediate position between the first gap position and the second gap position. The coil spring applies a force to the adjusting lever so as to keep a gap to be maintained at each gap position. Assuming that a small gap is to be maintained at the first gap position and a large gap is to be maintained at the second gap position, at the second gap position, the busing member is likely to rotate toward the first gap position side because of the weights of the carriage guide shafts and the carriage. Therefore, in order to surely maintain the second gap position, the force applied by the coil spring has to be made larger.
In a case of adjusting the gap by using the driving force of the motor, however, it is necessary to rotate the bushing member against the force applied by the coil spring. For example, in a case where the driving force is obtained from a motor that drives a feed roller for feeding the recording medium to rotate, the motor has to be selected considering the force applied by the coil spring, thus increasing the cost. Especially, in the gap adjusting device disclosed in Japanese Patent Application Laid-Open NO. 10-211748, the motor has the larger load.
In addition, in the conventional gap adjusting device described above, two gap positions, i.e., the first and second gap positions, are maintained by the coil spring. Therefore, three or more gap positions could not be provided.